1. Field of the Invention
The present invention is generally related to optically measuring distances and optically detecting objects and, more particularly, to a device and a method for optically measuring distances and optically detecting reflective surfaces.
2. Description of Related Art
One example of a conventional optical sensor 1 is illustrated in FIG. 1: A light beam 11 generated by a laser 2 impinges on an object 12 to be detected and is at least partially diffusely scattered there. Scattered light is received by a receiving lens system 3 at an angle α, which is dependent on the distance of the object from the sensor. The angle α is determined in the receiver. In correspondence with a maximum and a minimum determinable angle of incidence α, a measuring range m results, within which a distance of the object 12 is capable of being determined.
This method has the disadvantage that it does not work in case of reflective mirror-like surfaces because it is based on the diffuse scattering. Accurate detection of the position of reflective surfaces is, inter alia, necessary during the processing of silicon wafers. Here there is the difficulty, that these high-purity—and polished surfaces generate hardly any scattered light. However, scattered light is required by conventional optical sensors in order to detect an object.
As a solution there is the possibility of increasing the amount of scattered light with very powerful lasers and in this manner achieve detection. The disadvantage of the method lies in the hazards for the eyesight of the users that are created by the use of powerful lasers.
A further possibility consists in arranging the optical transmitter and receiver such that the light reflected from the reflective object is directly guided into the receiver. The drawback of this method is the fact that the transmitter, “mirror”, and receiver have to be very accurately aligned relative to one another.